The present invention relates to analysis tools for analyzing the ground, from a surface thereof, by means of a sonde, enabling the rocks contained in the ground to be analyzed, and more particularly it relates to analysis tools for analyzing rocks which surround a well, e.g. tools for determining both the distribution of the porosity of oil-bearing rocks, and their associated permeability.
Analysis sondes for analyzing both the distribution of the porosity of oil-bearing rocks, and their associated permeability, are already known. In general, such sondes have a resolution time of approximately one to three seconds. They are disposed facing the rocks to be analyzed and must, in theory, be maintained facing said rocks during a period of time that is not less than their resolution time. Concerning the height of the volume in which rocks are analyzed, which volume is referred to below as the xe2x80x9clobexe2x80x9d, said height can vary greatly depending on the structure of the sonde, e.g. from a few centimeters to more than a meter. Consequently, in order to be able to analyze rocks covering a significant height, it is necessary to displace the sonde along the wall of the well and carry out a large number of successive measurements.
Such is the case, for example, of the device described in U.S. Pat. No. 4,686,653 which, in an attempt to mitigate the above-mentioned drawbacks, uses two sondes, thereby considerably increasing the cost of the device, whilst nevertheless failing to give reliable comparable results because it uses two sondes, and consequently two different sensors which experience shows will never have responses that are identical and which can, in addition, be positioned differently down the well relative to the wall of the well, thereby emphasizing that it is almost impossible to check their positions relative to the wall. Furthermore, the device operates in a single sense only, i.e. when going down a well, which is almost impossible to do in a deep oil well or the like, for example.
In addition, in particular in the case of oil wells which are always very deep, the length of the cables necessary for moving the tools carrying the sondes does not enable the tools to be displaced step by step. With a sonde have a tall lobe, it is possible for the sonde to be driven to move in continuous translation at a determined speed without being held stationary during the resolution time, and the results that are obtained are then corrected by computation. It will therefore be understood that measurement accuracy depends on lobe height. Attempts have therefore been made in the art to provide analysis sondes having lobes of height that is as small as possible.
However, in particular in the oil industry, ground analysis must imperatively be performed in the shortest possible time. Sondes must be driven to move in continuous translation at a speed which is generally imposed by other considerations and which is generally too fast relative to sonde resolution time and lobe height for the corrections computed on the measurements to be able to lead to results that are reliable.
Thus, an object of the present invention is to provide an analysis tool for analyzing the ground by means of a sonde enabling the rocks contained in the ground to be analyzed, using sondes having given resolution times and lobes of relatively small height, and enabling the sondes to be driven at a relatively high average speed, while giving analysis results that are reliable and perfectly acceptable.
More precisely, the present invention provides an analysis tool for analyzing the ground, from a surface thereof, by means of a sonde having a determined analysis lobe and a resolution time equal to T, the tool being characterized by the fact that it comprises:
a drive head driven to move in continuous translation at a speed V relative to said surface of the ground and along a given direction parallel to said surface;
a skid;
means for associating the sonde and the skid so that the sonde can analyze the rocks contained in said lobe; and
means for coupling together the drive head and the skid so that the two elements can be displaced relative to each other along said direction over a distance having a value equal to D.